What are the basic preoperative (preop) laboratory tests?

Basic Preoperative Laboratory Testing

There is no universal "basic preop lab panel"—preoperative testing should be driven by clinical history, physical examination findings, comorbidities, and surgical risk rather than ordered routinely for all patients. 1, 2

Core Principle: Selective Testing Based on Risk Factors

The fundamental approach is to order tests only when findings would alter perioperative management. 1 Routine testing in healthy patients undergoing low-risk surgery is not beneficial and wastes resources, with an estimated $18 billion spent annually on preoperative testing in the U.S. 3

Complete Blood Count (CBC)

Order CBC selectively for:

• Patients with liver disease or hematologic disorders that increase anemia risk 1, 2
• History of anemia or recent blood loss 1, 2
• Anticipated significant perioperative blood loss 1, 2
• Cardiovascular surgery 1
• Patients older than 60 years undergoing neurosurgery 1
• ASA class 2 or 3 patients with cardiovascular or respiratory disease undergoing major surgery (grade 3 or 4) 1

Do not order CBC for: Healthy ASA class 1 patients younger than 40 years undergoing low-risk surgery 1

Electrolytes and Renal Function (Na+, K+, Creatinine, BUN)

Order electrolyte and creatinine testing for:

• Patients taking diuretics, ACE inhibitors, ARBs, NSAIDs, or digoxin 1, 2
• Hypertension, heart failure, chronic kidney disease, complicated diabetes mellitus, or liver disease 1, 2
• All patients with known renal conditions 1, 2
• All patients undergoing neurosurgery or cardiovascular surgery 1, 2
• ASA class 3 patients with cardiovascular disease 1
• ASA class 2 patients older than 60 years with cardiovascular disease undergoing intermediate surgery 1

Key caveat: Age alone should not drive testing decisions—clinical findings and medications are the determining factors. 1

Coagulation Studies (PT, aPTT, Platelet Count)

Order coagulation testing only for:

• Patients with liver disease or diseases of hematopoiesis 1, 2
• Patients taking anticoagulants (warfarin, clopidogrel, aspirin) 1, 2
• History of spontaneous bruising or excessive surgical bleeding 1
• Family history of heritable coagulopathy 1
• Physical examination findings suggesting coagulation disorder 1

Do not order: Indiscriminate coagulation testing is not warranted due to low prevalence of inherited coagulopathies, and routine tests may be normal even in von Willebrand disease. 1, 2

Glucose Testing

Order random glucose for:

• Patients at very high risk of undiagnosed diabetes based on history, examination, or medication use 1, 2

Order A1C (not random glucose) for:

• Patients with known diabetes, but only if results would change perioperative management 1, 2

Rationale: Random glucose reflects control over only a few hours and rarely alters management in known diabetics. The incidence of occult diabetes in presurgical populations is only 0.5%. 1, 2

Electrocardiogram (ECG)

Order ECG for:

• Patients with known heart disease, peripheral vascular disease, or cerebrovascular disease undergoing intermediate- or high-risk surgery 1, 2
• Patients with cardiovascular risk factors (coronary artery disease, heart failure, cerebrovascular disease, diabetes, renal insufficiency) undergoing vascular or intermediate-risk surgery 1, 2
• Patients older than 65 years 1
• Patients with diabetes, hypertension, chest pain, heart failure, smoking history, or peripheral vascular disease at any age 1

Do not order ECG for: Asymptomatic patients undergoing low-risk surgery 1, 2

Chest Radiography

Order chest X-ray for:

• Patients with new or unstable cardiopulmonary signs or symptoms 2, 4
• Patients at risk of postoperative pulmonary complications, only if results would change perioperative management 2

Do not order: Routine chest radiography for asymptomatic, otherwise healthy patients 2, 4

Urinalysis

Order urinalysis for:

• Patients undergoing urologic procedures 2
• Implantation of foreign material (prosthetic joint, heart valve) 2

Do not order: Routine urinalysis for asymptomatic patients 2

Special Population: Cataract Surgery

Order no preoperative testing for patients in their usual state of health undergoing cataract surgery. A randomized controlled trial of over 19,000 patients showed no difference in outcomes between tested and untested groups. 1, 2

Common Pitfalls to Avoid

• Same-day testing: Avoid ordering tests on the day of surgery—if abnormal results are found, surgery often proceeds anyway, making the testing pointless. 5, 6
• Testing healthy patients: Studies show 54-59% of patients with no comorbidities still receive unnecessary testing. 5, 6
• Ignoring medication history: Failure to identify patients on diuretics, ACE inhibitors, or anticoagulants leads to missed indications for appropriate testing. 1
• Age-based testing: Ordering tests based solely on age cutoffs rather than clinical risk factors wastes resources. 1

Evidence Quality Note

Research consistently demonstrates that neither preoperative testing nor abnormal results predict postoperative complications in low-risk ambulatory surgery patients. 5, 6 Only ASA classification, type of anesthesia, and type of operation strongly correlate with complications. 7